This invention relates to organic solvents with low .sup.13 C content.
The measurement of absorption spectra of chemical compounds in solution requires solvents having no absorption at all or only a minor absorption in the absorption range of the compound to be investigated.
A large number of solvents are available for infrared, ultraviolet and fluorescent spectroscopy, making it possible to measure spectra of chemical compounds in any desired spectral range. This also holds true for proton NMR spectroscopy, for which proton-free or deuterated solvents are commercially available in a large selection.
For several years, carbon-13 NMR spectroscopy has also been a widely popular auxiliary means for obtaining information on the structure of organic compounds. Informative carbon-13 NMR spectra can be measured of organic compounds whose carbon atom content of carbon having an atomic weight of 13 (.sup.13 C atoms) is above the natural content of 1.1 atom percent. However, the manufacture of such organic compounds is extremely cumbersome and expensive. Usually, such production is impossible in case of compounds of an unknown structure, for example, natural substances.
The development of the Fourier conversion nuclear resonance technique made it possible also to obtain useful .sup.13 C NMR spectra of organic compounds having the natural carbon-13 content. In this technique, the quality of the recorded spectrum is dependent on the strongest signal in the spectrum. In the normal case, the compound to be analyzed is utilized, for measuring the spectrum, as a solution in an organic solvent, which almost always is provided in a large excess and thus gives rise to the strongest signal of the spectrum. Therefore, especially in case of test substances which are of moderate or poor solubility, the amount of information extracted from a .sup.13 C NMR spectrum is adversely influenced to a considerable extent by the solvent. Although this effect can be extensively eliminated, to do so requires very efficient and thus expensive electronic computers.
It is an object of this invention to avoid the disadvantages in carbon-13 NMR spectroscopy caused by the inherent absorption of the solvents.